1. Field of the Invention
The invention relates to a split shaft gas turbine, and more particularly, to a variable vane and support assembly providing a confined flow path between the last stage of a gas generator and the first stage of the low pressure turbine thereof.
2. Description of the Prior Art
In certain applications, such as marine propulsion units, it is often desirable to have a gas turbine in which the speed of the power turbine can be varied independently of the speed of the gas generator. The gas turbine employed in such situations comprises a split shaft arrangement in which a compressor is driven by a turbine and a low pressure turbine drives a power take-off. The turbine and compressor are generally referred to as a gas generator. In operation, the above-named components are serially connected in an axial flow path initiating with the compressor, then to a combustor which in turn discharges to the high pressure turbine in slow communication with the low pressure turbine after which the working fluid is discharged.
The speed of the low pressure turbine can be varied by disposing within the flow path between the last stage of the high pressure turbine and the first stage of the low pressure turbine a nozzle vane capable of various angular settings to control the flow characteristics of the working fluid entering the low pressure turbine.
The variable nozzle vane is disposed adjacent to the first stage low pressure turbine blades at the terminal end of a confined passageway leading from the high pressure turbine discharge. The confined passageway is defined by stationary radially inner and outer wall members. Support for the inner wall member, in that it is adjacent rotating apparatus except for the outer wall member and the variable vanes, normally requires a strut extending through the flow path to support the inner wall from the outer wall. The strut introduces disturbances in the flow of the working fluid that reduce the overall efficiency of the turbine engine.